proc mulinv(int a, b) int:
    int t, nt, r, nr, q, tmp;
    if b<0 then b := -b fi;
    if a<0 then a := b - (-a % b) fi;
    t := 0; nt := 1; r := b; nr := a % b;
    while nr /= 0 do
        q := r / nr;
        tmp := nt; nt := t - q*nt; t := tmp;
        tmp := nr; nr := r - q*nr; r := tmp
    od;
    if r>1 then -1
    elif t<0 then t+b
    else t
    fi
corp

proc show(int a, b) void:
    int mi;
    mi := mulinv(a, b);
    if mi>=0
        then writeln(a:5, ", ", b:5, " -> ", mi:5)
        else writeln(a:5, ", ", b:5, " -> no inverse")
    fi
corp

proc main() void:
    show(42, 2017);
    show(40, 1);
    show(52, -217);
    show(-486, 217);
    show(40, 2018)
corp